Must be someone here who's taken guns to Australia could give some advice.

The Aussie Government probably doesn't have the cavalier attitude towards muzzleloaders than the US has. Even here, flintlocks are pretty much non-guns. Even people barred from owning firearms can own and hunt with flintlocks here and no federal licence is required.

I don't think I'd be too concerned about going after one of the Aussie bulls with a 14 bore double - 10 bore, of course, would be better, shooting a .750" or slighlty larger ball of about 600gr.+ in WW alloy, 635gr.+ in pure lead. The alloy'd ball would be the one to use on buff, though, no matter what bore size.